Re: Speed improvements in ZFS

On 8/20/23, Alexander Leidinger <Alexander@leidinger.net> wrote:
> Am 2023-08-20 22:02, schrieb Mateusz Guzik:
>> On 8/20/23, Alexander Leidinger <Alexander@leidinger.net> wrote:
>>> Am 2023-08-20 19:10, schrieb Mateusz Guzik:
>>>> On 8/18/23, Alexander Leidinger <Alexander@leidinger.net> wrote:
>>>
>>>>> I have a 51MB text file, compressed to about 1MB. Are you interested
>>>>> to
>>>>> get it?
>>>>>
>>>>
>>>> Your problem is not the vnode limit, but nullfs.
>>>>
>>>> https://people.freebsd.org/~mjg/netchild-periodic-find.svg
>>>
>>> 122 nullfs mounts on this system. And every jail I setup has several
>>> null mounts. One basesystem mounted into every jail, and then shared
>>> ports (packages/distfiles/ccache) across all of them.
>>>
>>>> First, some of the contention is notorious VI_LOCK in order to do
>>>> anything.
>>>>
>>>> But more importantly the mind-boggling off-cpu time comes from
>>>> exclusive locking which should not be there to begin with -- as in
>>>> that xlock in stat should be a slock.
>>>>
>>>> Maybe I'm going to look into it later.
>>>
>>> That would be fantastic.
>>>
>>
>> I did a quick test, things are shared locked as expected.
>>
>> However, I found the following:
>>         if ((xmp->nullm_flags & NULLM_CACHE) != 0) {
>>                 mp->mnt_kern_flag |=
>> lowerrootvp->v_mount->mnt_kern_flag &
>>                     (MNTK_SHARED_WRITES | MNTK_LOOKUP_SHARED |
>>                     MNTK_EXTENDED_SHARED);
>>         }
>>
>> are you using the "nocache" option? it has a side effect of xlocking
>
> I use noatime, noexec, nosuid, nfsv4acls. I do NOT use nocache.
>

If you don't have "nocache" on null mounts, then I don't see how this
could happen.

-- 
Mateusz Guzik <mjguzik gmail.com>